Substrate treatment method

ABSTRACT

Method for removing a portion of the binder phase from the surface of a substrate that is composed of particles of at least a first phase joined together by the binder phase, and wherein the surface is etched by contacting it with a gas flow of an etchant gas and a second gas. The second gas is one or more gases that will not react with the substrate or the removed binder phase and will not alter the oxidation state of the substrate during etching.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to a method for etching composite materialsubstrates and other substrates, and also is directed to a method forapplying wear-resistant and other coatings to composite materialsubstrates and other substrates. The present invention also relates tocomposite material substrates, which are comprised of particles of ahard constituent phase in a binder material phase that binds togetherthe hard constituent particles, having wear-resistant and othercoatings. The present invention finds application in any field in whichit is advantageous to enhance the adhesion of a wear-resistant and othertypes of coatings to substrates. Examples of fields of application ofthe present invention include the manufacture and treatment of dies usedin metal stamping, punching, threading, and blanking, and themanufacture and treatment of metal cutting inserts used in milling,turning, drilling, boring, and other metal removal operations.

BACKGROUND OF THE INVENTION

Composite materials comprised of particles of a hard constituent phaseand a binder phase binding the particles together are common and arereferred to as “composite materials” or “composite substrates”hereinafter. Such materials also may be referred to as “cemented”composite materials and include, for example, ceramics, cermets, andcemented carbides. Cemented carbides, include, for example, materialscomposed of a hard particulate material such as, for example, particlesof one or more of tungsten carbide (WC), titanium carbide (TiC),titanium carbonitride (TiCN), tantalum carbide (TaC), tantalum nitride(TaN), niobium carbide (NbC), niobium nitride (NbN), zirconium carbide(ZrC), zirconium nitride (ZrN), hafnium carbide (HfC), and hafniumnitride (HfN) cemented together by a binder phase that is composedpredominantly of one or more of cobalt, nickel, and iron.

Metal cutting inserts fabricated from composite materials are commonlyused in chip cutting machining of metals in the metal machiningindustry. Metal cutting inserts are commonly fabricated from particlesof metal carbide, usually tungsten carbide with the addition of carbidesof other metals such as, for example, niobium, titanium, tantalum, and ametallic binder phase of cobalt or nickel. The carbide materials providehigh strength but still may wear quickly when used in, for example,milling and other metal machining operations. By depositing a thin layerof wear-resistant material on the working surfaces of cemented carbidecutting inserts it is possible to increase the wear-resistance of theinserts without adversely affecting toughness. Commonly usedwear-resistant cemented carbide insert coatings include, for example,TiC, TiN, TiCN, and Al₂O₃. Such wear-resistant coatings reduce theerosion and corrosion of the inserts' binder material.

The utility of coated composite materials such as coated cementedcarbides is limited by the strength of adhesion of the wear-resistantcoating to the composite material. Absence of strong adhesion betweenwear-resistant coatings and metal cutting inserts causes delamination ofthe coatings from the inserts, decreasing the inserts' service life. Thepresence of cobalt at the inserts' surfaces also increases the tendencyof the coatings and substrates to experience delamination during use.Accordingly, it would be advantageous to provide a novel method forincreasing the adhesion of wear-resistant coatings to compositematerials. More broadly, it would be advantageous to enhance theadhesion of wear-resistant coatings and other types of coatings tocomposite material and other types of substrates.

SUMMARY OF THE INVENTION

The present invention provides a method for removing a portion of thebinder phase from a substrate that is composed of at least particles ofa first phase joined together by the binder phase. The present methodincludes the step of etching at least a portion of a surface of thesubstrate by contacting the surface with a gas flow that is composed ofat least an etchant gas and a second gas for a time period that willallow for removal of the desired amount of binder phase. The second gascomprises one or more gases that will not react with the substrate orthe removed binder material and that will not alter the oxidation stateof the substrate during the etching step. Preferably, the second gas isone or more gases that will not react with the substrate or the removedportion of binder material to form deposits of a phase of W_(x)Co_(y)C(wherein x=3-9 and y=2-6), also referred to herein as an η (eta) phase,on the substrate.

The etchant gas used in the present method may be any gas or combinationof gases that will suitable remove the desired portion of the binderphase from the substrate during the etching step. Possible etchant gasesinclude hydrogen chloride gas, H₂F₂ gas, and gaseous forms of any of theGroup VIIA elements. Other possible etchant gases useful in the presentmethod will be apparent to those having ordinary skill once apprised ofthe present invention. The second gas may be, for example, one or moregases selected from nitrogen gas, helium gas, argon gas, and neon gas.Preferably the gas flow is applied to the substrate during the etchingstep by introducing a flow of the etchant gas concurrently with a flowof the second gas into a chamber containing the substrate at a pressureand temperature, and for a time, that will result in removal of thedesired portion of the binder phase. In one particular application ofthe present method, the gas flow consists of concurrent flows ofhydrogen chloride gas and nitrogen gas.

Preferably, during the etching step binder phase is removed from asurface of the substrate to a depth of between about 3 microns to about15 microns, and more preferably to a depth of between about 4 microns toabout 6 microns.

The method of the present invention preferably is applied to substratescomposed of a composite material comprising particles of a hardconstituent material joined together by a binder material. Examples ofsuch composite materials include cemented carbides and cermets. Examplesof the binder material of such composite materials include materialscomposed of one or more materials selected from cobalt, nickel, iron,elements within Group VIII of the periodic table, copper, tungsten,zinc, and rhenium. Once apprised of the details of the presentinvention, one of ordinary skill in the substrate coating and treatmentarts will comprehend additional composite materials to which the presentinvention may be applied.

The present invention also is directed to a method for applying acoating to at least a portion of the surface of a substrate, preferablya composite substrate that includes hard constituent material particlesjoined together by a binder. The method is carried out by removing aportion of the binder from a surface of the substrate by contacting thesurface with a gas flow including an etchant gas and a second gas for aperiod of time that will remove the desired portion of binder. Thesurface etching effect of the etchant gas provides an etched surface onthe substrate, and the etched surface will include voids produced as thebinder is etched away from between hard constituent particles. Thesecond gas is one or more gases that will not react with the substrateor the portion of the binder removed from the substrate, and that willnot change the oxidation state of the substrate during the etchingprocess. Preferably, the second gas will not react during the etchingprocess to form eta phase within the voids etched in the substrate'ssurface. In a subsequent step of the method, a coating is applied to atleast a portion of the etched surface. At least a portion of the coatingis deposited within at least a portion of voids on the etched surfacecreated by removal.

Thus, the etching step of the present invention may be preceded orfollowed by one or more additional steps, including, for example, thestep of depositing a coating on the etched surface of the substrateproduced by the etching step. Because the coating infiltrates voids inthe etched surface of the substrate that have been produced by removalof binder material during the etching step, the adhesion of the coatingto the substrate is enhanced. Preferably, the coating is one thatenhances the wear resistance of the substrate, but it also may beselected from any other conventional substrate coating. Possiblewear-resistant coatings that may be applied in the coating step of thepresent method include those composed of, for example, one or more ofTiC, TiN, TiCN, diamond, Al₂O₃, MT-milling coating (described in detailbelow), TiAIN, HfN, HfCN, HfC, ZrN, ZrC, ZrCN, BC, Ti₂B, MoS, Cr₃C₂,CrN, CrCN, and CN.

The present invention is also directed to substrates that have beenproduced by the method of the present invention. For example, suchsubstrates within the scope of the invention may have an etched surfaceproduced by the foregoing etching step, and also may have a coating,wear-resistant or otherwise, which at least partially infiltrates voidsproduced in the substrate's surface by the etching step of theinvention. In particular, the present invention is directed to asubstrate composed of a composite material including particles of a hardconstituent material and a binder material. The substrate includes anetched surface portion having voids thereon produced by removing aportion of the binder material therefrom by contacting the surfaceportion with concurrent flows of at least a suitable etchant gas and asecond gas. The second gas must be incapable of reacting with thesubstrate or the removed binder material or changing the oxidation stateof the substrate during etching of the binder material. A coating may beadhered to at least a portion of the etched surface portion of thesubstrate, and at least a portion of the coating is deposited within atleast a portion of the voids provided in the etched surface portion.

Examples of applications of the method of the present invention includethe manufacture and treatment of wear resistant cutting inserts, dies,punches, and other elements used in applications such as: metalstamping, punching, threading, blanking, milling, turning, drilling,boring, and other metal removal operations; mining and oil drilling,including fabricating or treating mining and drilling bits used in longwall and coal boring miners, tricone, percussive and rooftop drillingbits, road planing and other like applications; wood workingapplications, including fabricating or treating bits and blades used insawing, planing, routing, shaping, and other woodworking applications;drawing, heading, and back extrusion, including the fabrication andtreatment of punches and dies used in such applications; rod mill rolls;and high corrosion environments. An example of a specific application ofthe present invention is in the manufacture and treatment of items madefrom tungsten-based alloys containing iron, nickel, copper and/orcobalt. Such items include, for example, aircraft weights, electricalcontact points, and electrodes.

The reader will appreciate the foregoing details and advantages of thepresent invention, as well as others, upon consideration of thefollowing detailed description of the invention. The reader also maycomprehend such additional details and advantages of the presentinvention upon practicing the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color.Copies of this patent with color drawing(s) will be provided by thePatent and Trademark Office upon request and payment of necessary fee.

The features and advantages of the present invention may be betterunderstood by reference to the accompanying figures, in which:

FIG. 1 is a photomicrograph of a prepared section of a metal cuttinginsert composed of SD-5 material coated with wear-resistant MT-milling(moderate temperature milling and turning) coating by the method of thepresent invention;

FIGS. 2a-2 c and 3 a-3 c are photomicrographs showing the condition ofan edge surface of each of three metal cutting inserts, composed of SD-5material and coated with an MT-milling coating by the method of theinvention, after 10 and 18 milling passes, respectively;

FIGS. 4a-4 c and 5 a-5 c are photomicrographs showing the condition ofan edge surface of each of three uncoated metal cutting inserts,composed of SD-5 material, after 10 and 18 milling passes, respectively;

FIGS. 6a-6 c are photomicrographs showing the condition of an edgesurface of three metal cutting inserts, composed of T-14 material andcoated with an MT-milling coating by the method of the invention, after4 milling passes;

FIGS. 7a-7 c are photomicrographs showing the condition of an edgesurface of three metal cutting inserts composed of T-14 material, eachinsert both unetched and uncoated, after 4 milling passes;

FIG. 8 is a photomicrograph of a metal cutting insert composed of H-91material and coated with an MT-milling coating by the method of thepresent invention;

FIGS. 9 is a photomicrograph showing the condition of a metal cuttinginsert, composed of H-91 material and coated with an MT-milling coatingby the method of the invention, after one milling pass;

FIG. 10 is a photomicrograph showing the condition of a metal cuttinginsert, composed of H-91 material and coated with an MT-milling coatingof TiN/TiCN/TiN layers totaling approximately 5 microns (applied byCVD), after one milling pass; and

FIGS. 11a-11 d are photomicrographs of a prepared section of a heavymetal part containing tungsten metal particles (about 90 weight percentof the part's total weight) suspended in an iron/nickel binder (about 10weight percent of the part's total weight) that was etched and coatedwith an MT-milling coating by the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

An aspect of the present invention is directed to a method for applyinga coating, preferably a wear-resistant coating, to a composite materialsubstrate. The composite material substrate includes a phase of a hardconstituent and also includes a binder phase that is predominantly oneor more of cobalt, nickel, and iron. The present inventors havediscovered that the method of the invention enhances the adherence ofthe coating to the composite material substrate and inhibitsdelamination of the coating. The present invention also is directed toetched and etched/coated substrates prepared by the method of thepresent invention.

It is believed that in relation to the known composite materialsubstrate coating methods, the present method improves adhesion betweencomposite material substrates and wear-resistant coatings by allowingthe coatings to infiltrate the surface of the substrate. To accomplishthis, a portion of the binder phase of a surface region of the compositematerial substrate is removed by a novel etching procedure, preferablyto a depth in the range of about 3 to about 15 microns (inclusive),while leaving the hard constituent particles in the surface regionsubstantially intact. Wear-resistant coatings applied to compositematerial substrates that have been etched by the present methodinfiltrate the voids in the surface region created by removal of thebinder phase. The infiltration of the coating is believed to increasethe adhesive strength between the coating and the composite materialsubstrate. It has been found that the enhanced adhesion between coatingsand composite material substrates achieved by the present method reducesdifferences in thermal expansion between the substrates and coatings,improves the coatings' resistance to deformation, increases coating wearresistance, and reduces the occurrence of thermal cracking.

As used herein, “composite material” refers to a material, in any form,that includes at least particles of a phase of a hard constituentmaterial and a phase of a binder material that binds together the hardconstituent particles. The composite material may be, for example,cemented carbides and cermets. The binder material of the presentcomposite material may include one or a combination of more than one ofcobalt, nickel, copper, and iron. In addition to cobalt, nickel, copper,and/or iron, the binder material may include other elements andcompounds as are known in the art. Such other elements include, forexample, those within Group VIII of the periodic table (elements havingatomic numbers 26-28, 44-46, and 76-78), tungsten, zinc, and rhenium.The particles of the hard constituent may be, for example, particlescomposed of:

one or more carbide materials selected from tungsten carbide (WC),titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC),vanadium carbide (VC), chromium carbide (Cr₃C₂), molybdenum carbide(MoC), and iron carbide (FeC);

one or more carbonitrides and/or nitrides of one or more of therefractory metals, including carbonitrides of one or more of W, Ti, Ta,Nb, V, Cr, Mo, and Fe;

one or more oxides and/or borides of one or more of aluminum, zirconium,and magnesium; and

one or more of tungsten, molybdenum-based materials, and tungsten-basedmaterials.

As used herein, the term “refractory metals” refers to metals having anextremely high melting point, for example, W, Mo, Ta, Nb, Cr, V, Re, Ti, Pt, and Zr.

In addition to enhancing the adhesion of wear-resistant coatings to theforegoing composite materials, it is believed that the method of thepresent invention also may be used to enhance the adhesion ofwear-resistant and other types of coatings to other types of materials,including, for example, heavy metals, sialons, Si₃N₄, and compositeceramics, that have a phase that may be etched by the present method.The identities of such other materials may be readily determined bythose having ordinary skill in the substrate coating arts. Moreover,although the following examples are directed to the application ofwear-resistant coatings to composite material and other substrates, itwill be understood that the present method also may be used to betteradhere other types of coatings to such substrates. Such other coatingsinclude coatings that impart desirable properties to the substratesurface, such as, for example, coatings that enhance the substrate'sresistance to corrosion, including oxidation, or that provide aparticular surface appearance to the substrate. The identities of othercoatings that may be applied using the method of the present inventionwill be readily apparent to those having ordinary skill in the substratecoating arts once apprised of the invention.

In one embodiment of the method of the present invention, the methodgenerally includes at least the following steps:

1. Place a composite material substrate to be coated in a chamber of achemical vapor deposition furnace.

2. Etch away all or a portion of the binder phase in a surface region ofthe composite material substrate to a depth of about 3 microns to about15 microns by contacting the surface region with a mixture comprising anetchant gas and an inert gas such as nitrogen gas. (The etchant gas maybe selected from, for example, gaseous hydrogen chloride, gaseous H₂F₂,or the gaseous form of any of the Group VIIA elements. Other suitableetchant gases will be apparent to those of ordinary skill in the art ormay be determined by such persons without undue experimentation, and itwill be understood that the identity of such suitable alternativeetchant gases will depend on the particular composition of the materialthat is to be etched. The gaseous mixture is applied to the surface ofthe material to be etched under conditions and for a time suitable toremove the desired amount of binder phase from the material. Suchconditions and times may be readily ascertained, without significantexperimentation, by those having ordinary skill in the substrate coatingarts.)

3. Purge the chamber with a flow of an inert gas (“inert” meaning thatit will not react with the binder material) such as, for example,nitrogen, argon, or helium gas.

4. Coat the etched region of the composite material substrate with atleast one layer of a wear-resistant material by introducing a reactivegaseous form of the wearresistant material into the chamber underconditions that will result in the deposition of the wear-resistantmaterial on the etched region. (Such conditions, which generally includesuch parameters as reactive gas flow rates, chamber gas pressure,chamber and/or substrate temperature, and reaction time) may be readilyascertained by those having ordinary skill in the substrate coating artsonce apprised of the present invention.

Although the method of the invention is disclosed above as being carriedout in a chamber of a chemical vapor deposition (CVD) furnace, it willbe understood that the etching step may be carried out in any chamberthat is sealed from the environment and into which a flow of the gasesmay be introduced. An advantage of carrying out the process in a CVDfurnace is that the etching, purging, and coating steps may be carriedout sequentially in the furnace chamber without the need to move thecomposite materials from one chamber to another during the process.Thus, the method of the invention may be programmed as a complete cyclein the CVD furnace and accomplished in one run. This feature of theinvention provides a distinct advantage over procedures wherein a liquidsolution etchant is used to remove binder phase material because suchliquid solutions cannot be introduced into the same chamber employed tocoat the substrate by a CVD or PVD process. Also, it has been found thatthe substrate may be kept cleaner and the depth of etching may be bettercontrolled when using a gaseous etchant as opposed to a liquid etchant.

The step of etching binder phase from the composite material substratepreferably should remove binder material to a depth of about 3 to about15 microns and more preferably about 4 to about 6 microns, into thesubstrate surface. Too shallow an etching depth does not provide asignificant enhancement in coating adhesion. Too great an etching depthweakens the surface of the substrate. Etching time may be varied toaccount for differences in the susceptibility of the particular binderphase to be removed by the etchant gases. Those having ordinary skill inthe substrate coating arts may readily determine the etching timenecessary to provide a desired depth of etching for a particularsubstrate. The substrate temperature at which the etching step should becarried out to remove the desired amount of binder material also willdepend upon the character of the binder, but may be readily determined.

Deposits of a phase of W_(x)Co_(y)C (wherein x=3-9 and y=2-6), alsoknown as η (eta) phase, may form on the surface of composite materialsubstrates. Eta phase is a hard and brittle carbon-deficient phase thatmay easily fracture and may be produced when etching substrates thatinclude tungsten, carbon, and cobalt. The presence of eta phasesignificantly degrades the properties of composite material substratesused in material removal (i.e., cutting, drilling, threading, boring,etc.) applications and, therefore, the generation of eta phasepreferably should be avoided during the etching and coating of compositematerial substrates and other substrates by appropriately adjusting theetching and coating conditions. For example, relative to compositematerial substrates including nickel binder, composite materialsubstrates having cobalt binder should be etched at lower substratetemperatures in order to inhibit the formation of eta phase on thesurface of the substrate. The inventors also have determined that ifhydrogen gas is present during an etching step employing a gaseousetchant, the hydrogen may combine with any carbon present as WC and anycobalt within the substrate material and will thereby make the WCdeficient in carbon, resulting in formation of an eta phase. Onepossible reaction representative of formation of an eta phase is asfollows:

3WC_((s))+4H_(2(g))+3Co_((s))→2CH_(4(g))+W₃Co₃C_((s))

The eta phase does not convert to CoCl₂, as is required for theprecursor elements of the eta phase to leave the substrate surface as agas. The inventors have concluded that formation of eta phase issignificantly inhibited when using nitrogen or certain other gases insubstitution for hydrogen gas used in conjunction with etchant gasduring the etching step. A representation of a possible reactionoccurring during etching of a cobalt-containing composite material by ahydrogen chloride etchant gas, and wherein the etchant gas is notapplied to the material in combination with hydrogen gas, is believed tobe as follows:

Co_((s))+HCl_((g))→CoCl_(2(g))+H_(2(g))

The CoCl₂ is a gaseous product that is swept from the coating furnaceduring the purging step.

Accordingly, the inventors have discovered that the step of etching asubstrate including tungsten, carbon, and a binder phase includingcobalt will not be satisfactorily accomplished if the gaseous etchantmixture includes hydrogen gas. For example, when etching binder phasefrom a composite material cutting insert composed of tungsten carbideparticles in a binder composed predominantly of cobalt using a gaseousetchant mixture of hydrogen chloride and hydrogen gases, cobalt residueremains in the voids etched between the tungsten carbide particles andthe undesirable eta phase may form, significantly reducing substratetoughness. The inventors have found that nitrogen gas may beadvantageously substituted for hydrogen gas to prevent formation of etaphase. More broadly, to better ensure removal of etched binder materialso as to avoid formation of eta phase on substrate surfaces, gases thatmay be substituted for hydrogen gas in the gaseous mixture used in thesubstrate etching step include those selected from one or more ofnitrogen gas and other gases that do not react with the substrate orremoved binder and that do not change the oxidation state of thesubstrate. Such other gases are believed to include, for example,helium, argon, and neon gases.

The foregoing representations of reactions that may occur during theetching process are provided only to better illustrate possible reactionmechanisms, and should not be considered to in any way limit the scopeof the invention.

As discussed above, the etchant gas that may be used in the etching stepof the method of the present invention may be any gas that will suitablyremove the desired depth of binder phase in a surface region of thecomposite material substrate that is being etched. Such etchant gasesinclude, for example, HCl gas, H₂F₂ gas, and the gaseous form of any ofthe Group VIIA elements in the periodic table of the elements.

The purging step occurring subsequent to the etching step is necessaryto remove any products of the etching reaction and any etchant remainingin the chamber, and to reduce any explosion hazard. Any gas orcombination of gases that will suitably remove the reactant products andremaining etchant gases and that will not react with the binder or hardparticle constituents of the composite material may be used as thepurging gas. Suitable purging gases include, for example, one or more ofnitrogen, helium, and argon gases.

Once etched, the substrate may then be coated with a wear-resistant orother coating material by any conventional composite substrate coatingprocess. Such processes include, for example, CVD, PVD, plasma arc, andsuper lattice processes. Still other composite material coatingprocedures will be readily apparent to those of ordinary skill in thesubstrate coating arts. All such other suitable coating processes may beused in the present method subsequent to the gas etching procedure. Anycoating process used to deposit wear-resistant material on a compositematerial substrate etched by the procedure of the present method iscarried out under conditions by which the wear-resistant material may atleast partially infiltrate the voids in the composite material createdby removal of the binder material. One of ordinary skill may readilydetermine such conditions without undue experimentation.

On a basic level, the present invention also is directed to a method forremoving binder material from a region of a composite material, and theinventive method need not include the subsequent coating step. Acomposite substrate having a roughened surface may be produced by such amethod. Roughened composite substrates may be used in a variety of knownapplications, including, for example, ball point pen balls, wherein aroughened surface provides enhanced traction. Additionally, substratesmay be etched by the present method and then coated at some later timeand/or at a different facility, rather than in a single procedure inwhich the etching and coating steps are combined. One example of acoating that may be applied in a procedure removed in time from theetching procedure and/or at another facility is a diamond coating.

Following are actual examples illustrating embodiments of the method ofthe present invention. The following examples are illustrative examplesonly, and should not be considered to in any way limit the scope of thepresent invention.

Example 1

A Bernex 250 CVD coating furnace was prepared by introducing into thecoating chamber of the furnace a 10 l/min (liters/minute) flow ofhydrogen gas to establish a 200 mbar hydrogen gas pressure within thechamber. The chamber was then heated to 850° C. A cemented carbidesubstrate composed of H-91 grade material available from Stellram,LaVergne, Tennessee, was placed in the prepared furnace chamber and thechamber atmosphere was heated to 850°. H-91 grade material is composedof 88.5 weight percent tungsten carbide, 11.0 weight percent cobalt, and0.5 weight percent of a mixture of TiC, TaC, and NbC. The materialexhibits a hardness of 89.7 HRA, 14.40 g/cc density, and a transverserupture strength of approximately 389,000 psi.

The flow of hydrogen gas was then stopped, and a concurrent flow of 20l/min nitrogen gas and 1 l/min hydrogen chloride gas was introduced intothe chamber to provide a chamber pressure of 800 mbar. Binder was etchedto a depth of approximately 5 microns into the substrate's surface bythe running the concurrent N₂/HCl gas flow into the chamber for 25minutes, and then discontinuing the flow of HCl gas. While maintainingthe chamber atmosphere at 850° C., the chamber was then purged for 15minutes by continuing the 20 l/min flow of N₂ gas while establishing a60 mbar chamber pressure.

After purging the chamber, and without removing the etched substratefrom the chamber, the etched substrate was coated with a moderatetemperature milling and turning coating (referred to herein as“MT-milling coating”), which is a multi-layer insert coating consistingof two TiN layers of approximately 1 micron with a TiCN layer ofapproximately 3 microns disposed between the two TiN layers. TheMT-milling coating was deposited on the substrate by introducing intothe furnace chamber flows of gases that will produce coatings of TiN,TiCN, and then TiN, in that order, as follows.

Before the coating procedure began, the chamber atmosphere was heated to920° C. and the chamber pressure was reset to 160 mbar. After thatpressure was established, a first TiN layer was provided on thesubstrate by initiating a 9 l/min nitrogen gas flow, increasing thehydrogen gas flow to 14 l/min, and initiating a 2.1 ml/min flow of TiCl₄gas. The concurrent flows of the three gases were allowed to proceed for60 minutes while the chamber pressure was maintained at approximately160 millibars. During the 60-minute period, the furnace temperature waslowered 5-10° C. every fifteen minutes so as to be at approximately 895°C. at the end of the period.

The interposed TiCN coating was produced by lowering the nitrogen gasflow to 8 l/min, and then resetting chamber pressure to 60 mbar. TheTiCl₄ gas flow was then raised to 2.4 ml/min. Once all flows wereconstant, a flow of CH₃CN gas generated by vaporizing a 0.3-0.4 ml/minflow of liquid CH₃CN flow was initiated. The concurrent gas flows werecontinued for 2 hours, during the first hour of which the furnacetemperature was reduced to 870° C. At the end of the 2-hour period, theflows of CH₃CN and TiCl₄ gases were discontinued.

To prepare for deposition of the second TiN layer, the flow of nitrogengas was discontinued, chamber pressure was set to 500 mbar, hydrogen gasflow was reset to 12 l/min, and furnace temperature was set at 940° C.When that temperature was reached, the pressure was set to 60 mbar,hydrogen gas flow was reset to 10.5 l/min, nitrogen gas flow was resetto 4.5 l/min, and TiCl₄ gas flow was reset to 1.4 ml/min. On reachingthe target 1.4 l/min TiCl₄ gas flow rate, the flows were continued attemperature for 30 minutes, at which time the pressure was reset to 800mbar and the gas flows were continued for an additional 30 minutes. Thefurnace was then purged by shutting off the TiCl₄ gas flow, resettingchamber pressure to 600 mbar, raising hydrogen gas flow to 12 l/min, andlowering nitrogen gas flow to 3.5 l/min. The reset gas flows werecontinued for fifteen minutes. The furnace was then subjected to a cooldown procedure.

It was observed that the MT-milling coating infiltrated at least aportion of the voids etched in the substrate's surface.

Example 2

The Bemex 250 CVD furnace used in Example 1 was prepared using theprocedure described in that example. A cermet substrate composed of SD-5material, but having the same size and shape as the substrate in Example1, was placed into the coating furnace and the furnace atmosphere washeated to 920° C. SD-5 material is a cermet grade material availablefrom Stellram, LaVergne, Tenn., and is composed of TiCN and Mo₂Cparticles in a Co/Ni binder. SD-5 material has the approximate elementalcomposition 45.2 Ti, 22.6 Mo, 10.9 C, 2.3 N, 19.0 Ni, and exhibits thefollowing approximate mechanical properties: 91.8 HRA hardness, 6.30g/cc density, and a transverse rupture strength of 300,000 psi. Afterheating the furnace atmosphere to 920° C., the Co/Ni binder was thenetched to a depth of 5 microns from the substrate's surface usingconcurrent flows of hydrogen chloride and nitrogen gases at the flowrates, pressure, and reaction time used in Example 1 above. The furnacechamber was then purged using a 20 l/min flow of N₂ gas for 15 minutesat a chamber pressure of 60 millibars. The etched composite was thencoated with an MT-milling coating using the procedure of Example 1. TheMT-milling coating infiltrated the etched voids to a depth of 5microns±approximately 1 micron, and with approximately 1 micron of thecoating disposed above the substrate's surface.

Example 3

Three Stellram cutting inserts of type SEKN-42-AF4B composed of SD-5material (as described in Example 2) were first etched and then coatedwith the MT-milling coating by the following procedure.

A CVD furnace chamber was prepared using the procedure described inExample 1. The SD-5 cutting inserts were then inserted into the furnacechamber and were etched using the procedure of Example 2. Once etched,the inserts were coated with MT-milling coating by the procedure ofExample 1. The MT-milling coating produced on the etched inserts by theforegoing procedure was approximately 5 microns in thickness and thesurface TiN layer infiltrated the voids etched in the inserts' surfaces.Approximately 5 microns of the coating extended above the inserts'surfaces. FIG. 1 is a photomicrograph (2040X) of a preparedcross-section through the surface of one of the etched and coated SD-5inserts. The photomicrograph shows the infiltration of the MT-millingcoating into the voids etched in the insert surface. The infiltration ofthe coating into the voids increased the adherence of the coating to theinsert and improved the thermal shock resistance of the coating.

The three etched and coated SD-5 inserts and three inserts of the sametype that were unetched and uncoated were inserted at one time into asix-insert Teledyne (Lavergne, Tenn.) HSM-3E4-45 EZ shear cutter thatwas then installed on a 2 H.P. Bridgeport milling machine and testedunder the following milling conditions:

8620 steel at 20-25 Rockwell C hardness

800 surface feet per minute

0.050 inch depth of cut

0.004-0.005 inches per tooth (feed rate)

16.5 inch length of cut

2.5 inch width of cut

The SD-5 inserts were pulled and inspected after every two 16.5 inchmilling passes. After the initial two passes, one uncoated SD-5 inserthad one thermal crack started and the five remaining SD-5 inserts didnot exhibit thermal cracks. After ten passes, all threeunetched/uncoated SD-5 inserts exhibited one or more thermal crackswhile only one etched and coated SD-5 insert exhibited a single thermalcrack. Milling testing was concluded after 18 passes, at which pointeach unetched/uncoated insert exhibited 2-4 thermal cracks on their usededges, while only one thermal crack existed in one etched and coatedinsert. The conditions of an edge surface of each of the threeetched/coated SD-5 inserts after 10 and 18 passes are shown in FIGS.2a-c and 3 a-c, respectively. The used edge conditions of the threeunetched/uncoated SD-5 inserts after 10 and 18 passes are shown in FIGS.4a-c and 5 a-c, respectively.

Example 4

Three Stellram SEKN-42-AF4B cutting inserts composed of T-14 materialwere etched and then coated with an MT-milling coating by the methodused in Example 3. T-14 material is a milling grade material availablefrom Stellram (LaVergne, Tenn.) having a nominal composition composed of70 weight percent tungsten carbide and 20 weight percent of acombination of tantalum carbide, niobium, and titanium carbide.Particles of the foregoing material are bound together by a cobaltbinder that is 10 weight percent of the total weight of the material.T-14 material typically exhibits a hardness of 91.20 HRA, 12.43 g/ccdensity, and an average transverse rupture strength of 296,000 psi.

The three etched and coated T-14 inserts and three unetched and uncoatedT-14 inserts of the same type were inserted at one time into asix-insert HSM-3E4-45 EZ shear cutter, installed on a 2 H.P. Bridgeportmilling machine, and tested under the following milling conditions:

4140 steel at 40-45 Rockwell C hardness

500 surface feet per minute

0.050 inch depth of cut

0.004-0.005 inch per tooth (feed rate)

14 inch length of cut

2.5 inch width of cut

After four passes under the above conditions, the depth-of-cut regionsof the etched and coated T-14 inserts showed no evidence of thermalcracking or deformation as examined under a 40X microscope. After fourpasses all unetched and uncoated T-14 inserts exhibited numerous thermalcracks with one insert at the thermal crack breakout stage. As usedherein, “thermal crack breakout” is the point at which two or morethermal cracks connect and just before the insert surface fractures.Photomicrographs showing the condition of the depth-of-cut region of thethree etched and coated T-14 inserts and the three unetched and uncoatedT-14 inserts are shown in FIGS. 6a-c and 7 a-c, respectively. The testdemonstrated that using the present invention's method to etch compositesubstrates with cobalt binder to a 10 micron depth and then coating thesubstrates provides for a coated insert showing significant edgestrength and enhanced resistance to coating/edge delamination, coatingspalling, and edge fracture. Results similar to the SD-5 insert millingtests of Example 3 were achieved in that the T-14 substrates etched andcoated by the present invention's method provide an increased resistanceto thermal cracking of the cobalt-based material.

Example 5

Stellram SEKN-42-AF4B type cutting inserts composed of H-91 gradematerial were obtained. Half of the H-91 inserts were coated withMT-mill coating in a Bernex 325 furnace using an automated proceduresubstantially similar to the above-described MT-milling coatingprocedure so as to provide a layered coating on the inserts composed ofapproximately 1 micron TiN, approximately 3 microns TiCN, and then 1micron TiN, all such thicknesses being approximate. The remaining H-91grade inserts were etched in a Bemex 250 CVD furnace using the procedureof Example 1 and the etched inserts were then MT-milling coated in thefurnace by the procedure described in Example 3. Actual total MT-millingcoating thicknesses were determined to be 6.2 microns for theunetched/coated inserts and 5.4 microns for the etched/coated inserts. Aphotomicrograph of the coated surface of one of the etched and coatedH-91 inserts is shown in FIG. 8. The figure demonstrates theinfiltration of the coating into the etched inserts' surfaces.

Single etched/coated or unetched/coated H-91 inserts were installed on aseven-insert Teledyne HSM-5E4-45 5-inch diameter EZ shear cutter,installed on a 25 H.P. Kearney-Trecker milling machine, and tested underthe following milling conditions:

ASTM A536 (F-33100 unified UNS) nodular cast iron

875 surface feet per minute

0.125 inch depth of cut

0.008 feet per tooth

20 inch length of cut

4 inch width of cut

Each insert was pulled after one pass and examined. After one pass, eachof the tested unetched/coated inserts exhibited 6-7 thermal cracks,while the tested inserts that had been etched and coated by the methodof the present invention exhibited only a single thermal crack. 30Xphotomicrographs of an etched/coated H-91 insert after one milling passand an unetched/coated insert after one milling pass are provided asFIGS. 9 and 10, respectively.

This example 5 compared inserts composed of identical base materials andidentical coatings, with the only significant difference being that thetest samples of one set were first etched by the present method and theMT-milling coating had infiltrated the resulting interstices in theinserts' surfaces. The etched and infiltrated inserts exhibitedsignificantly increased resistance to thermal cracking relative to theunetched coated inserts.

Example 6

A heavy metal part containing 90 weight percent tungsten metal particlessuspended in 10 weight percent of an iron/nickel binder was etched andcoated with an MT-milling coating using the procedures of the inventionas generally described in the foregoing examples involving insertcomposed of SD-5 material. 21X photomicrographs of sections of theetched and coated metal part taken through the coated surface are shownin FIGS. 11a-11 d. The photomicrographs shown the infiltration of thecoating into the voids etched in the metal part's iron-nickel binder.

In each of the foregoing Examples 1-5, all composite material substratesthat were etched using the method of the present invention failed toshow evidence of the formation of an eta phase.

Those of ordinary skill in the substrate coating and treatment arts willappreciate that various modifications and changes in the details of theinvention that has been disclosed herein may be made without detractingfrom the advantages provided by the invention, and it will be understoodthat all such changes and modifications remain within the principle andscope of the invention as expressed in the appended claims.

We claim:
 1. A method for applying a coating to at least a portion ofthe surface of a substrate, the substrate comprising particles of a hardmaterial in a binder phase, the method comprising the acts of: removinga portion of said binder phase from said surface of said substrate bycontacting said surface with a gas flow substantially free of hydrogengas and comprising an etchant gas and a second gas for a period of timethat will remove said portion of said binder phase to thereby provide anetched surface on said substrate, said etched surface comprising voidsproduced by removal of said portion of said binder phase, said secondgas comprising one or more gases that will not react with said substrateor said portion and that will not change the oxidation state of saidsubstrate during removal of said portion of said binder phase; andapplying said coating to at least a portion of said etched surface, atleast a portion of said coating being deposited within at least aportion of said voids in said etched surface.
 2. The method recited inclaim 1 wherein said second gas will not react with said substrate orsaid binder phase removed from said surface during said removing act toform an eta phase within said voids on said etched surface.
 3. Themethod recited in claim 1 wherein said second gas is one or moreselected from nitrogen gas, helium gas, argon gas, and neon gas.
 4. Themethod recited in claim 1 wherein said etchant gas is one or moreselected from hydrogen chloride gas, H₂F₂ gas, F₂ gas, Cl₂ gas, Br₂ gas,and l₂ gas.
 5. The method recited in claim 4 wherein said gas flowcomprises concurrent flows of hydrogen chloride gas and nitrogen gas. 6.The method of claim 1 wherein in said etching step said binder phase isremoved from said surface to a depth of between about 3 microns to about15 microns.
 7. The method of claim 6 wherein in said etching step saidbinder phase is removed from said surface to a depth of between about 4microns to about 6 microns.
 8. The method of claim 1 wherein saidsubstrate is selected from cemented carbides and cermets.
 9. The methodof claim 8 wherein said hard constituent material comprises one or morematerials selected from the group consisting of: a carbide materialselected from the group consisting of tungsten carbide, titaniumcarbide, tantalum carbide, niobium carbide, vanadium carbide, chromiumcarbide, molybdenum carbide, and iron carbide; a carbonitride of arefractory metal; a nitride of a refractory metal; a carbonitride of anelement selected from the group consisting of W, Ti, Ta, Nb, V, Cr, Mo,and Fe; an oxide of an element selected from the group consisting ofaluminum, zirconium, and magnesium; a boride of an element selected fromthe group consisting of aluminum, zirconium, and magnesium; and amaterial selected from the group consisting of tungsten, amolybdenum-containing material, and a tungsten-containing material. 10.The method of claim 1 wherein said binder phase comprises one or morematerials selected from the group consisting of cobalt, nickel, iron,elements within Group VIII of the periodic table, copper, tungsten,zinc, and rhenium.
 11. The method of claim 1 wherein said hardconstituent material comprises tungsten carbide and wherein said binderphase comprises cobalt.
 12. The method of claim 1 wherein said act ofremoving occurs within a chamber into which said gas flow is introduced.13. The method of claim 1 wherein said coating enhances the wearresistance of said substrate.
 14. The method of claim 13 wherein saidcoating is comprised of one or more materials selected from the groupconsisting of TiC, TiN, TiCN, diamond, Al₂O₃, TiAIN, HfN, HfCN, HfC,ZrN, ZrC, ZrCN, Cr₃C₂, CrN, and CrCN.
 15. The method of claim 13 whereinsaid coating is an MT-milling coating.
 16. The method of claim 1wherein: said substrate is selected from the group consisting of metalcutting inserts, dies, punches, stamps, threading devices, blankingdevices, milling devices, turning devices, drilling devices, boringdevices, mining bits, drilling bits, tricone bits, percussive bits, roadplaning devices, wood working bits, wood working blades, drawingdevices, heading devices, back extrusion devices, rod mill roll devices,and wear parts used in corrosive environments; and said coating enhancesthe wear resistance of said substrate.
 17. The method of claim 16wherein said coating is an MT-milling coating.
 18. A method for applyinga coating to a substrate, the method comprising: providing a substratecomprising particles of a hard material in a binder phase; contacting atleast the surface of said substrate with a gas flow free of hydrogengas, said gas flow comprising an etchant gas and a second gas, tothereby remove at least a portion of said binder phase from said surfaceand provide voids in said surface, said second gas consisting of one ormore gases that will not react with said substrate and that will notchange the oxidation state of said substrate during removal of saidportion of said binder phase; and applying a coating to at least aportion of said substrate so that said coating is at least partiallydisposed within at least a portion of said voids.
 19. A substratecoating method comprising: providing a substrate including particles ofa hard material in a binder phase; removing at least a portion of saidbinder phase from said surface of said substrate by contacting saidsurface with a gas flow comprising an etchant gas and at least oneadditional gas for a period of time sufficient to remove said portion ofsaid binder phase and to thereby provide an etched surface on saidsubstrate, said etched surface comprising voids produced by removal ofsaid portion of said binder phase, said gas flow free from any gas thatwill react with said substrate or said portion or will change theoxidation state of said substrate during removal of said portion of saidbinder phase; and applying a coating to at least a portion of saidetched surface, at least a portion of said coating being depositedwithin at least a portion of said voids in said etched surface.